TY - JOUR

T1 - Influence of Sample Gas Humidity on Product Ion Formation in High Kinetic Energy Ion Mobility Spectrometry (HiKE-IMS)

AU - Schaefer, Christoph

AU - Schlottmann, Florian

AU - Kirk, Ansgar T.

AU - Zimmermann, Stefan

N1 - Funding Information: Funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – 318063177 and 390583968.

PY - 2022/6/1

Y1 - 2022/6/1

N2 - High Kinetic Energy Ion Mobility Spectrometers (HiKE-IMS) chemically ionize gaseous samples via reactant ions and separate the generated ions by their motion in a neutral gas under the influence of an electric field. Operation at reduced pressures of 10-40 mbar allows for reaching high reduced electric field strengths (E/N) of up to 120 Td. At these high E/N, the generated ions gain the namesake high kinetic energies, leading to a decrease in cluster size of the reactant ions by increasing the reaction rate of collision-induced cluster dissociation of hydrates. In positive ion polarity and in purified air, H 3O +(H 2O) n, NO +(H 2O) n, and O 2 +•(H 2O) pare the most abundant reactant ions. In this work, we investigate the effect of varying sample gas humidity on product ion formation for several model substances. Results show that increasing the sample gas humidity at high E/N of 120 Td shifts product ion formation from a charge transfer dominated reaction system to a proton transfer dominated reaction system. For HiKE-IMS operated at high E/N, the reduction in cluster size of reactant ions allows ionization of analytes with low proton affinity even at high relative humidity in the sample gas of RH = 75% at 303.15 K and 1013.25 hPa. In contrast to conventional IMS, where increasing the sample gas humidity inhibits ionization for various analytes, increasing sample gas humidity in HiKE-IMS operated at 120 Td is actually beneficial for ionization yield of most analytes investigated in this work as it increases the number of H 3O +(H 2O)n.

AB - High Kinetic Energy Ion Mobility Spectrometers (HiKE-IMS) chemically ionize gaseous samples via reactant ions and separate the generated ions by their motion in a neutral gas under the influence of an electric field. Operation at reduced pressures of 10-40 mbar allows for reaching high reduced electric field strengths (E/N) of up to 120 Td. At these high E/N, the generated ions gain the namesake high kinetic energies, leading to a decrease in cluster size of the reactant ions by increasing the reaction rate of collision-induced cluster dissociation of hydrates. In positive ion polarity and in purified air, H 3O +(H 2O) n, NO +(H 2O) n, and O 2 +•(H 2O) pare the most abundant reactant ions. In this work, we investigate the effect of varying sample gas humidity on product ion formation for several model substances. Results show that increasing the sample gas humidity at high E/N of 120 Td shifts product ion formation from a charge transfer dominated reaction system to a proton transfer dominated reaction system. For HiKE-IMS operated at high E/N, the reduction in cluster size of reactant ions allows ionization of analytes with low proton affinity even at high relative humidity in the sample gas of RH = 75% at 303.15 K and 1013.25 hPa. In contrast to conventional IMS, where increasing the sample gas humidity inhibits ionization for various analytes, increasing sample gas humidity in HiKE-IMS operated at 120 Td is actually beneficial for ionization yield of most analytes investigated in this work as it increases the number of H 3O +(H 2O)n.

KW - high kinetic energy ion mobility spectrometry

KW - humidity

KW - ion mobility spectrometry

KW - ionization

KW - moisture

UR - http://www.scopus.com/inward/record.url?scp=85131216835&partnerID=8YFLogxK

U2 - 10.1021/jasms.2c00099

DO - 10.1021/jasms.2c00099

M3 - Article

VL - 33

SP - 1048

EP - 1060

JO - Journal of the American Society for Mass Spectrometry

JF - Journal of the American Society for Mass Spectrometry

SN - 1044-0305

IS - 6

ER -